Fiber Optic Monitoring System Research Articles

Crack monitoring for municipal sewer pipes using DFOST

The distributed fiber optic sensing technique (DFOST) provides an effective solution for long-term deformation monitoring of sewer pipelines under operation conditions due to occurrence of cracks. However, optical fibers attached on the pipeline wall might fail to capture all cracks as they are usually highly spatially scattered, resulting in misjudgment of pipe structural conditions. To address this challenge, this paper presents a novel deployment approach of distributed fiber optic monitoring system for pipeline cracks. First, the working principle of optical frequency domain reflectometry (OFDR) is explained. Second, the production of concrete pipe specimens with different optical fiber sensors deployment schemes is shown in detail. Finally, a comprehensive analyse of the results of visual inspection and fibre optic monitoring is completed. To evaluate the performance of this approach, experimental data from various cases were considered. The conclusion of this paper provides theoretical and empirical support for the application of distributed fiber optic sensors for pipeline cracks monitoring.

Sparrow search mechanism-based effective feature mining algorithm for the broken wire signal detection of prestressed concrete cylinder pipe

To enhance the capability of distributed optical fiber (DOF) monitoring system on real-time broken wire signal detection of prestressed concrete cylinder pipe (PCCP), this research proposes a novel effective parameter mining algorithm by utilizing wrapper theory and sparrow search algorithm (SSA). First, the improvement approach of SSA is investigated by applying the adaptive adjustment strategy, the Gaussian mutation perturbation, and the Tent chaotic perturbation. The subset search method is constructed based on the improved SSA (ISSA). Second, the similarity degrees of vibration signals are characterized by the Euclidean distance and the average linkage distance. On this basis, the subset evaluation criterion is established according to the classification accuracy of hierarchical clustering (HC). Finally, the prototype experiment is conducted in which the phase-sensitive optical time-domain reflectometry (Φ-OTDR) monitoring system is employed to collect vibration signals. Then, the effectiveness and the performance of the developed methodology are validated. The following results are drawn. (1) Benchmark function tests indicate that the convergence performance, the optimization ability, and the operation stability of ISSA are superior to those of SSA and the improved particle swarm optimization (IPSO). (2) The original set that has 122 feature parameters is established, and ISSA-HC, IPSO-HC, and SSA-HC extract 24, 31, and 55 effective parameters, respectively. (3) The recognition accuracies of the 3 parameter subsets are 95.83%, 84.17%, and 80.83%, respectively. The parameter subset mined by ISSA-HC has the best pattern recognition ability. This research provides technical support for the broken wire monitoring of in-service PCCP engineering. Meanwhile, it offers a foundation for further developing suitable pattern recognition algorithms to identify PCCP broken wire signals.

Research on the variation law of floor stress information entropy in upper protective layer mining based on Brillouin optical fiber sensing

The characteristics of floor failure and stress changes during the mining process of protective layers are crucial for determining the effectiveness of pressure relief. Three boreholes were designed in the 21104 fully mechanized mining face of Hulusu Coal Mine to implant optical fibers into the floor of the working face. A fiber optic monitoring system was established to monitor the dynamic evolution of stress in the floor rock mass at different mining distances. Based on the information entropy in information theory, the monitoring results in the fiber optic monitoring system are calculated to obtain the stress information entropy at different mining distances. A quantitative dynamic analysis is conducted on the stress change process of the mining floor rock layer, and the stress change law of the protective layer after mining is verified through numerical calculation and similar simulation experiments. The results indicate that the evolution of stress information entropy can be divided into four stages, namely the original rock stress stage, stress concentration stage, stress release stage, and stress recovery stage. The stress information entropy shows a fluctuating upward trend, indicating that coal seam mining leads to a decrease in the orderliness of the overlying rock system and an increase in disorder. In different spatial evolution processes, there are also significant differences in stress information entropy. In the vertical direction, the entropy value of shallow rock layers changes greatly, while the entropy value of deep rock layers changes slightly. Mining leads to a decrease in the orderliness of the entire overlying rock system, an increase in stress information entropy, and a fluctuating upward trend in stress information entropy. The information entropy of overlying rock deformation and re compaction increases, but the degree of change of the former is greater than that of the latter. The Brillouin fiber optic sensing technology provides a new method for monitoring the stress changes in the protective layer mining floor, achieving quantitative analysis of floor rock failure.

Subsurface multi-physical characterization of mountain excavation and city construction in loess plateau with a fiber-optic sensing system

Mountain excavation and city construction (MECC) projects being launched in the Loess Plateau in China involve the creation of large-scale artificial land. Understanding the subsurface evolution characteristics of the artificial land is essential, yet challenging. Here, we use an improved fiber-optic monitoring system for its subsurface multi-physical characterization. The system enables us to gather spatiotemporal distribution of various parameters, including strata deformation, temperature, and moisture. Yan'an New District was selected as a case study to conduct refined in-situ monitoring through a 77 m-deep borehole and a 30 m-long trench. Findings reveal that the ground settlement involves both the deformation of the filling loess and the underlying intact loess. Notably, the filling loess exhibits a stronger creep capability compared to underlying intact loess. The deformation along the profile is unevenly distributed, with a positive correlation with soil moisture. Water accumulation has been observed at the interface between the filling loess and the underlying intact loess, leading to a significant deformation. Moreover, the temperature and moisture in the filling loess have reached a new equilibrium state, with their depths influenced by atmospheric conditions measuring at 31 m and 26 m, respectively. The refined investigation allows us to identify critical layers that matter the sustainable development of newly created urban areas, and provide improved insights into the evolution mechanisms of land creation.

Distributed optical fiber sensing technology in operation status monitoring of GIL equipment

Abstract This paper firstly proposes distributed fiber optic sensing technology based on big data technology and physics, distributed fiber optic sensing technology includes distributed fiber optic sensing technology based on interference type and distributed fiber optic sensing technology based on the scattering principle. Then investigated the demand for remote monitoring of distributed fiber optic sensing systems and the demand for large sensing networks in the Internet of Things and designed a long-distance distributed fiber optic sensing-based intelligent monitoring system. Finally, the vibration acceleration signal of the metal shell when partial discharge occurs is collected, and the high-frequency components in the vibration acceleration signal are used to diagnose and analyze the discharging faults caused by the metal particles of GIL. The results show that: when the rated current is loaded on the GIL, the main frequency distribution of the vibration acceleration signal on the surface of the metal shell is from 0 to 1 kHz, and the percentage of the signal energy in this frequency band is greater than 99% of the total energy in the range of 0 to 20 kHz. In the frequency range of 1 kHz to 20 kHz, the percentage of the signal energy in the total energy does not exceed 1%, and there is almost no high-frequency vibration acceleration signal. This study and the combination of these two technologies is a great contribution to the further development of each, but also more favorable for application in work and life.

Life Cycle Monitoring of Offshore Steel Pipe Piles via UWFBG Wireless Sensor Network

Monitoring the stress and deformation state of offshore steel pipe piles is very necessary for complex ocean environments. However, challenges still remain in remotely capturing detailed data on offshore projects. Herein, an ultraweak fiber Bragg gratings- (UWFBGs-) based wireless sensor network was established to obtain the high-precision strain along the piles. The No. 3 offshore wind power safety monitoring project in South Shandong Peninsula, China, used such a fiber-optic monitoring system. From January 1 to June 1, 2022, strain profiles of three offshore steel pipe piles were measured in seconds with a 1 m spatial resolution and a 1 με strain resolution, which clearly show sea level and mud-water interfaces. To assess the pile’s operational condition, the displacement and rotational angle of the mud surface are further calculated. It is discovered that the horizontal deformation at sea has a positive correlation with the wind, waves, and current, meanwhile decreasing with depth. The UWFBG-wireless sensor network can realize dynamic monitoring and early warning, which is promising for the life cycle monitoring of offshore wind turbine steel pipe piles.

FIBRADIKE, a novel distributed fiber optic monitoring system for dikes and earth dams

Safety issues related to climate change are one of the major challenges of modern society. One of the most significant risks is represented by extreme flood events which could lead to dike or earth dam breaching with catastrophic consequences for the environment. Despite the relevance of these infrastructure and modern advanced sensing technologies, dike and earth dam safety monitoring is carried out as it has been for centuries with visual inspections. In the best case, traditional point sensors, like piezometers, are installed in some limited sections. In this way it is not possible to early identify problem sections, which can be located many km away from the observation point. In this research an attempt has been made in order to develop a distributed fiber optical sensing system for dike and earth dam safety monitoring. The core of the system is represented by a novel distributed pore water pressure sensing unit, in the form of a specifically designed fiber optic sensing cable.. The development and first promising results of laboratory testing carried out on the industrially produced prototypes of the sensing cable are presented in this paper.

Study on stress-deformation mechanism of concrete face rockfill dam based on centrifugal model test

The traditional method of tracking the deformation of centrifugal dam model involves burying marker points on the sidewalls, which is commonly used. However, the method is inaccurate in monitoring the deformation of the model since the constraining effect of boundary effect on the model. In this study, a quasi-distributed fiber optic monitoring system was constructed using fixed-point distributed fiber Bragg grating. Particle image velocimetry, earth pressure cell, and other electromagnetic sensors were combined to examine the rationality of the face rockfill dams centrifugal model tests. Through comparative analysis, the applicability and stability of the fixed-point distributed FBG technique in the centrifugal model test were demonstrated. It is also demonstrated that traditional monitoring methods will underestimate the deformation of face rockfill dams by 2.32 % ∼ 13.55 %. This study addresses the shortcomings of existing monitoring methods with excessive measurement errors and provides a more applicable monitoring tool for developing related experimental studies.

Inverse flow zone characterization using distributed temperature sensing in a deep geothermal production well located in the Southern German Molasse Basin

Abstract. The localization and characterization of hydraulically active zones in a geothermal well is a major task in understanding the hydro geothermal reservoir. This is often done based on interpretations of spinner flow meter measurements that are performed at the end of the well test while injecting cold water. Once a production well is equipped with an electric submersible pump, data collection inside the reservoir and monitoring of the flow zones is usually barely possible. In a 3.7 km (MD) deep geothermal production well in Munich, Germany, it was successfully demonstrated in 2019 that a permanently installed optical fiber cable could close this measurement gap. We used this fiber-optic monitoring system to collect distributed temperature data once the well was set into production. We inversely modeled the inflow from the formation into the borehole from the production temperature data with an energy and mass balance model. The derived flow profile correlates with previous flow meter analysis and indicates that a karstified region at the very top of the reservoir is the driving factor for hydraulics and obtained production temperature. Qualitatively, the two profiles acquired by distributed temperature sensing (DTS) and flow meter are matchable, yet the production inflow profile by DTS logging is more differentiated compared to spinner flow meter logs interpretation during injection.

Evaluation and design of changes in optical cable and fibre optic online monitoring system based on digital communications technology

Evaluation and design of changes in optical cable and fibre optic online monitoring system based on digital communications technology

Evaluation and design of changes in optical cable and fibre optic online monitoring system based on digital communications technology

Evaluation and design of changes in optical cable and fibre optic online monitoring system based on digital communications technology

Experimental Tests of a Full Analog Fiber Optic Monitoring System Suitable for Safety Application at CERN

In this work, experimental tests of a full analog fiber optic monitoring system are reported. The proposed concept is conceived to satisfy the constrains imposed to be used for safety application, in terms of robustness and reliability, due to full passive optical devices and an analog-based circuitry. Moreover, it is compatible with the stringent requirements imposed by the Detector Safety System (DSS) of the Compact Muon Solenoid (CMS) experiment at CERN. From the optical side, the main device is the Arrayed Waveguide Grating (AWG), with the aim to filter and address the optical signal through a determined output channel, that is then transduced in electrical by means of a photodiode. From the electronic side, the designed board has the purpose to manipulate the signal in order to have an increasing monotone output current, in the range 4-20 mA, standard widely employed in safety system environment. In this way, the circuit gain can be set in order to match the value to the physical quantity under monitoring threshold. To give proof of its characteristics, the system is subjected to many test led at CERN, in which two Fiber Bragg Grating (FBG) sensors are under test into a custom climate box. Step temperature variation, as well as fast oscillating test and long term stability measurement are reported, confirming its key strength and field-validating it.

Comparative Assessment and Experimental Validation of a Prototype Phase-Optical Time-Domain Reflectometer for Distributed Structural Health Monitoring

Dynamic characterization and Structural Health Monitoring (SHM) are crucial tools, of increasing demand, for reliable operation and predictive maintenance of large infrastructures, as the percentage of critically ageing infrastructures is growing steadily. We present a minimally invasive and synchronous fiber optic monitoring system for SHM, based on Phase-Optical Time-Domain Reflectometry (Phase-OTDR), and we assess its applicability and performance on a modular Bailey-type bridge of 1 : 2.5 scale. Phase-OTDR systems, along with other fiberoptic-distributed techniques have proven their capabilities in long-range SHM applications, although their complexity and high cost limits drastically their applicability and SHM market penetration. Here, we propose the use of a prototype Phase-OTDR system, featuring customized interrogation instrumentation with a balanced trade-off between performance and cost. Its experimental validation is achieved by comparison with well-established commercial monitoring systems, such as Ground-Based Radar Interferometer (GBRI), laser tracker, and multipoint optical Fiber Bragg Gratings (FBGs), in various excitation conditions and structure-damage scenarios, easily implementable in the model bridge. Finite-element modelling (FEM) and simulations were employed to study the bridge behaviour and provide a reference and comparison framework for the experimental characterization. The Phase-OTDR system successfully detected the structural behaviour in an efficient distributed manner, demonstrating comparable performance to commercial point sensor systems, thus demonstrating its application potential.

Online evaluation method for the performance of in-service fiber optic strain monitoring systems

Online evaluation method for the performance of in-service fiber optic strain monitoring systems

A Quasi-Distributed Optical Fiber Monitoring System for Movement of Roof Strata in Mines

A Quasi-Distributed Optical Fiber Monitoring System for Movement of Roof Strata in Mines

In situ measurement of rockfill dam settlement using fiber optic gyroscope monitoring system

In situ measurement of rockfill dam settlement using fiber optic gyroscope monitoring system

Highly sensitive fiber optic microseismic monitoring system for tunnel rockburst

By capturing the micro-crack signals of rock mass structure, the microseismic (MS) monitoring technology is a good candidate for the forecasting and early warning of dynamic disaster. In this paper, MS sensors based on fiber optic interferometric scheme are studied and fabricated, and authors develop an 8-channel highly sensitive fiber optic MS system based on space division multiplexing technology to monitor the whole process of rock mass from micro-fracture to macro-damage. Field test of the system is carried out in Hanjiang River to Weihe River Water Diversion Project. The results show that it can realize continuously monitored with high accuracy and reliability in the tunnel and obtain the characteristic of temporal-spatio-strong of MS events, which are superior to the commercialized electrical monitoring equipment. This work shows that using fiber optic interference technology to develop accelerometer for MS monitoring system is both advantageous and feasible with the character of intrinsically safe.

Shallow seafloor seismic wave monitoring using 3-component fiber optic interferometric accelerometer

A fiber optic interferometric seismic monitoring system developed by us was deployed on the shallow seafloor near the Wuchang oceanic monitoring station off the Hainan Island, in the South China Sea, in 2017. In the past three plus years, it has recorded more than 40 teleseismic activities of magnitude 6.0+. We analyze these shallow seafloor observed seismic signals monitored by the fiber optic interferometric three-component accelerometer from the perspective of analyzing the underwater ambient seismic noise and the attenuation of the noise in the shallow seafloor seismic signals. The ambient seismic noise produced by wind, wave, shipping, and on-shore manmade activities admixed in the seismic signal is analyzed and discussed in detail. And the attenuation of such noise in the shallow seafloor seismic data using a hybrid denoising algorithm is demonstrated by applying it to three representative seismic events having different distances and magnitudes, with results showing that the noise in the shallow seafloor seismic signal is effectively reduced, and the ratio of the maximum acceleration value of seismic wave to the noise level is improved by more than 32 dB, rendering the seismic waves clearly observable.

Monitoring cold water injections for reservoir characterization using a permanent fiber optic installation in a geothermal production well in the Southern German Molasse Basin

Fiber optic sensing has gained importance for wellbore monitoring and reservoir characterization in geothermal fields as it allows continuous, spatially highly resolved measurements. Distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) technologies, among others, enable monitoring of flow regimes and heat transport inside the wellbore to describe the dynamical behavior of the reservoir. The technically challenging installation of a permanent fiber optic monitoring system in a geothermal production well over the entire wellbore length was conducted for the first time at the geothermal site Schäftlarnstraße in Munich, Germany. One cable with two DAS fibers, two DTS fibers, and one fiber for a downhole fiber optic pressure/temperature gauge were clamped to ¾-in. sucker rods and installed to 3.7 km measured depth to collect data from the wellbore after drilling, during testing, and during operations. We present DTS profiles during 3 months of well shut-in and show the results of two cold water injection tests conducted to localize inflow zones in the reservoir and to test the performance of the fiber optic setup. A vertical displacement in temperature peaks of approximately 1.5 m was observed during the injection tests, presumably resulting from thermal contraction of the sucker rod–cable setup. This was verified by analyzing the strain information from the DAS records over 1 h of warm-back after cold water injection with the calculated theoretical thermal contraction of DTS of the same period. We further verified the flowmeter measurements with a gradient velocity analysis of DTS profiles during injection. Intake to the major inflow zone was estimated to 93.5% for the first injection test, respective 94.0% for the second, intake of flowmeter was calculated to 92.0% for the same zone. Those values are confirmed by analyzing DTS profiles during the warm-back period after the well was shut.

Study of seismoacoustic effects in an producing oil horizontal well based on a fiber-optic cable sensor DAS

The possibilities of using distributed remote optical fiber-optic acoustic DAS cable-sensors for horizontal production wells for the purpose of directional seismic-acoustic profiling of sections in the inter-well space had been studied. For the first time, a seismic reaction to the shutdown of neighboring production wells had been recorded using stationary permanent fiber-optic monitoring systems. The conditions for the successful implementation of seismicacoustic crosswell sounding on the developed oil deposits had been determined.